MSP430FR5869: Could not read data from SPI

Hi all, I would like to read and write data into MSP430FR5869 over SPI with slave mode. But the read process always return 0 or 255.

My source code on MSP430 as below:

//select spi gpio

P2SEL0 |= BIT4 | BIT5 | BIT6;

UCA1CTLW0 |= UCSWRST;

UCA1CTLW0 |= UCMSB+UCSYNC;

UCA1CTLW0 &= ~UCSWRST;

UCA1IE |= UCRXIE;

UCA1IE |= UCTXIE;

I don't get why the SPI on MSP only able to write but failed to read.

Thanks, Cong Nga Le